The central 5-HT antagonist activity of 5 newer antihistaminics (chlorprothixene, chlorpentixol, diphenylpyraline, cyproheptadine, and mebhydrolin) has been studied and all of them have been found to possess central anti - 5-HT activity. These drugs have also been screened by the metrazol threshold test and all the five have been found to increase the toxicity of metrazol. A possible correlation between potentiation of metrazol toxicity and central anti-5-HT activity of these drugs has been discussed. It has been suggested that these drugs should be avoided or be given with caution while treating the patients of petit mal epilepsy for allergic manifestations.